+--------+      +--------+     +---------+
| alice  |      |  bob   |     |  carl   |
|        |      |        |     |         |
+--------+      +--------+     +---------+
     |               |              |     
     |-----hello---->|              |     
     |               |              |     
     |<----jello-----|              |     
     |               |              |     
     |--------------bye------------>|     
     |               |              |     
